Microphone position and speech level sensor

ABSTRACT

Improper microphone position and speech level on a telephone headset is sensed by comparison of a speech envelope to multiple signal threshold levels. A first threshold is used to determine whether a headset user is talking. A second threshold is used to determine whether a signal level at the microphone is sufficiently strong for proper communication. An indicator is activated when the user is talking and the signal level is too weak. Typically, a weak signal is caused by a mispositioned microphone or a user talking too softly.

BACKGROUND OF THE INVENTION

A. Technical Field

The present invention relates generally to the proper operation oftelephone headsets and other communication devices. Specifically, thepresent invention relates to the identification of a voice signal from amicrophone in a headset or communication device that is too weak and thesubsequent notification of the weak signal to a user.

B. Background of the Invention

Communications headsets typically have a microphone positioned on anadjustable arm that allows a user to move the microphone to a desiredposition, which the user finds comfortable. However, the adjustable armmay also be mispositioned without the user's knowledge. This problemoccurs most notably with users who have little experience and/ortraining in the proper use of communications headsets.

Effective use of a communications headset requires that the microphonebe positioned within a particular distance from the user's mouth. Theimportance of properly positioning a microphone is amplified when highquality noise canceling microphone headsets are used. A mispositionednoise canceling microphone experiences a reduction of sensitivity to theuser's voice, but its sensitivity to background noise remains the same.In either case, the microphone's signal to noise ratio (the ratio of theuser's voice to ambient noise) decreases, thereby reducing the overallquality of the voice signal or rendering the voice signal unintelligibleat the receiver side.

The use of a headset allows a user to perform other tasks while having aconversation. For example, telemarketers often use headsets because itallows the use of a computer during a conversation. Oftentimes, becauseof various distractions like the use of a computer during aconversation, a user does not talk loud enough to ensure a sufficientsound quality at the receiver side. As was the case with a mispositionedmicrophone, the user is unaware of the poor sound quality at thereceiver side until the listener verbally indicates the problem.

Attempts to remedy poor sound quality have focused on reducing thesignal to noise ratio at the receiver side. For example, U.S. Patent No.5,091,954, entitled “Noise Reducing Receiver Device,” (hereinafterSasaki) uses a feedback mechanism on an amplifier in a telephonereceiver to adjust the transfer function of the amplifier. The transferfunction is shifted to remove ambient noise in the signal. However,Sasaki is designed for situations where the signal to noise ratio isabove a specific level. If for example, the microphone is grosslymispositioned or the user is talking extremely quietly, then the signalmay be too weak for the amplifier to function properly. As a result, atalker-side solution is required for a mispositioned microphoneidentification device.

U.S. Pat. No. 4,777,649, entitled “Acoustic Feedback Control ofMicrophone Positioning and Speaking Volume,” (hereinafter Carlson)describes an apparatus coupled to a telephone handset that will detectwhen a handset is either too close or too far from a user's mouth.Specifically, a circuit determines whether the handset is mispositionedusing multiple comparators. A first comparator is used to determinewhether the handset is too far by comparing a voice signal from ahandset microphone to a first threshold. If the signal is weaker thanthe first threshold than the microphone is too far. A second comparatoris used to determine whether the handset is too close by comparing avoice signal from the handset microphone to a second threshold. If thesignal is strong than the second threshold than the microphone is tooclose. A switch is used to turn off the voice feedback into the handsetspeaker when the microphone is mispositioned, that is, when the signalis either below the first threshold or above the second. As a result, ifthe microphone is properly positioned then the user will hear his/herown voice in the handset speaker. However, if the microphone ismispositioned, the user will not hear his/her voice in the handsetspeaker.

Carlson's use of the user's own voice as the indication of whether themicrophone is mispositioned results in inherently limited quality andreliability. For example, if Carlson's circuit were to malfunction, thehandset itself would be almost inoperable because the user could nothear his/her voice in the handset speaker. Second, the notificationdirectly interrupts the use of the handset which reduces the quality ofthe conversation because the handset's feedback into the earpiece may beactivated multiple times during a conversation causing an uncontrollabledistraction to the handset user. As mentioned above, these limitationsare caused by the fact that Carlson does not detect speech levels belowan audible threshold. As a result, there is a need for a mispositionedmicrophone identification device that senses when a user is actuallyspeaking below an audible threshold so that a microphone mispositionindication may be provided by a device not implementing the talker'sactual voice (i.e., voice feedback).

Accordingly it is desirable to provide a microphone position and speechlevel sensor that operates on the talker-side and senses when a user isactually talking.

As described above, at least a portion of Carlson's circuit is embeddedin the handset itself. Specifically, the voice feedback mechanism isoperating within the earpiece and is inseparably coupled to the earpiececircuitry. As a result, a handset may not be upgraded to includeCarlson's mispositioning circuitry; rather the entire handset must bereplaced. This upgrade would be very expensive for companies who use alarge number of handsets. For example, telemarketing companies require alarge number of handsets or headsets and replacing all of these would becostly.

Accordingly, it is desirable to provide a microphone position and speechlevel sensor that may be used to upgrade pre-existing headsets orhandsets.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies and limitations of theprior art by providing a system and method for identifying amispositioned microphone and/or a corresponding improper speech level ata telephone headset microphone. In particular, the present inventionprovides a talker-side implementation that compares a voice signal froma headset microphone to two thresholds in order to detect whether aheadset user is talking and the signal level at the microphone issufficiently strong. These comparisons are typically done in parallelbut may also be done in sequence. A weak signal is generally indicativeof the microphone being incorrectly positioned or the user talking toosoftly. It is important to note that the present invention may beimplemented in a variety of other communication devices that require auser's mouth to be properly positioned to a microphone. For example, theinvention may be used in a telephone handset, cellular phone, ormicrophone in a PA system.

In one embodiment, the first threshold is used to determine when a useris actually talking. This first threshold represents an ambient noiselevel typical of an environment in which the headset is being used. Afirst comparator receives a voice signal from the microphone andcompares it to the first threshold. If the voice signal is stronger thanthe first threshold, then a user is actually talking into themicrophone. If the voice signal is weaker than or equal to the firstthreshold, then a user is not talking.

The second threshold is used to determine whether the voice signal istoo weak. This second threshold represents levels that are ordinarilyattained only by speech at adequate levels. A second comparator receivesa voice signal from the microphone and compares it to the secondthreshold. If speech peaks within the voice signal are consistentlystronger than the second threshold, then the microphone is properlypositioned. If the voice signal is weaker than or equal to the secondthreshold, then the signal-to-noise ratio of the voice signal at themicrophone is too low to provide sufficient quality at a user side ofthe telephone call. Either a microphone being mispositioned or a usertalking too quietly typically causes this weak voice signal.

An indicator is coupled to the comparators and used to signal a userwhen a voice signal is too weak. Logic (e.g., hardware or software)controlling the indicator receives data from each comparatorrepresenting (1) whether a user is talking and (2) whether acorresponding voice signal is too weak. If a user is talking but thevoice signal is too weak (i.e., the voice signal is above the firstthreshold and below the second threshold), the logic activates theindicator to signal the user to either adjust the microphone or talklouder. This indicator may be a visual indicator or an auditoryindicator.

The features and advantages described in this summary and the followingdetailed description are not all-inclusive, and particularly, manyadditional features and advantages will be apparent to one of ordinaryskill in the art in view of the drawings, specification, and claimshereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system including an adjustable headset, telephoneand telephone adapter in accordance with one embodiment of the presentinvention.

FIG. 2A illustrates a telephone headset adapter containing an improperspeech level indicator.

FIG. 2B illustrates a telephone headset adapter and a plug-in improperspeech level or accessory.

FIG. 3 illustrates a simplified block diagram of an improper speechlevel sensing circuit.

FIG. 4A illustrates a graphical representation of an improper speechlevel at a microphone resulting in a signal level between a noisethreshold and an audible threshold.

FIG. 4B illustrates a graphical representation of a user not talkingresulting in a signal level below an ambient noise threshold comprisingbackground noise.

FIG. 4C illustrates a graphical representation of proper speech level ata microphone resulting in a signal level above an audible threshold.

FIG. 5 illustrates a detailed diagram of improper speech level detectioncircuitry according to the present invention.

FIG. 6 illustrates a general flow diagram for sensing an improper speechlevel at a microphone on a headset.

FIG. 7 illustrates a specific flow diagram showing a first method forsensing and indicating an improper speech level at a microphone on aheadset.

The figures depict a preferred embodiment of the present invention forpurposes of illustration only. One skilled in the art will readilyrecognize from the following discussion that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles of the invention described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the invention. It will be apparent, however, to oneskilled in the art that the invention can be practiced without thesespecific details. In other instances, structure and devices are shown inblock diagram form in order to avoid obscuring the invention. Referencesto numbers without their subscripts (e.g., 205) are understood toreference all instances of the subscripted numbers. Moreover, it shouldbe noted that the language used in this disclosure has been principallyselected for readability and instructional purposes, and may not havebeen selected to delineate or circumscribe the inventive subject matter,resort to the claims being necessary to determine such inventive subjectmatter.

A. Overview of Microphone Position and Speech Level Sensor

The present invention is directed towards a talker-side device thatmeasures the strength of a voice signal from a microphone. Themicrophone may be positioned on an adjustable or fixed arm on acommunications headset or in a telephone handset. Additionally, thepresent invention may operate on a PA system comprising a microphone orany other device requiring a microphone to be properly positioned inrelation to a talker's mouth. Although an embodiment is described asoperating in a telephone headset system, the present invention's systemsand methods should not be limited to this embodiment. Rather, thepresent invention may operate in relation to any communication devicerequiring a speech level above a particular threshold at a microphone.As best shown in FIG. 1, one embodiment of the present invention is usedwithin a telephone headset system.

A telephone headset system generally comprises a headset 120, atelephone adapter 105, and a telephone 100 as well as connectionsbetween the devices. The headset 120 includes a speaker 140 that isplaced near the ear of a headset user. As shown in FIG. 1, a headband125 is used to hold the speaker against a user's ear, though in otherembodiments, earbud or earhook headsets may also be used. A microphone130 is attached to the end of an arm 135 and the arm is coupled to theheadband 125. This arm 135 may be adjustably mounted on the headband 125so that the position of the microphone 130 can be moved. This featureallows the headset to fit many different people because the adjustablemicrophone may be correctly positioned relative to a user's mouth.

The headset 120 may be electrically coupled to a headset adapter 105 vialine 110. The headset adapter 105 receives a signal from the microphone130 on the headset 120 and transmits a signal to the speaker 140 on theheadset 120. It is important to note that these signals may betransmitted wirelessly by transceivers on both the headset 120 andheadset adapter 105, and hence line 110 should be understood to includeeither a wire connection or a wireless connection, e.g., radio, infraredIn any event, a signal from the microphone representative of a user'svoice is transmitted from the headset 120 to the headset adapter 105.The headset adapter 105 is also electrically coupled to a telephone 100.Therefore, the headset adapter 105 functions as an interface between thetelephone 100 and the telephone headset 120. Additionally, the headsetadapter 105 may have other functions such as operating as a switchbetween the telephone headset 120 and a handset on the telephone 100.

FIG. 2A shows a first embodiment of the present invention functioningwithin a telephone adapter 105. As shown, a telephone adapter 105contains at least two interfaces. A first interface 220 connects atelephone headset 120 to amplification, rectification and envelopedetection circuitry 215 within the telephone adapter 105. An example ofa first interface 220 is a telephone jack that allows a telephoneheadset line to plug into the telephone adapter 105 and communicate withthe amplification, rectification and envelope detection circuitry 215.The first interface 220 may include other types of connection interfacesthat allow data to be transmitted between the telephone headset 120 andthe telephone adapter 105 such as a wireless transceiver. The firstinterface 220 is also coupled to a second interface 225 that connectsthe telephone adapter 105 to the telephone 100. This second interface225 is generally a telephone jack or other hard-wire connection.

The amplification, rectification and envelope detection circuitry 215comprises a buffer amplifier, a full-wave rectifier and a precisionenvelope detector and is coupled to threshold comparators and improperspeech level detection circuitry 210. This amplification, rectificationand envelope detection circuitry 215 receives a voice signal from thetelephone headset 120 via the first interface and outputs a speechenvelope signal representative of the voice signal. This speech envelopesignal may then be analyzed to determine whether a telephone headsetuser is talking and whether the voice signal level is sufficiently high.

The threshold comparators and improper speech level circuitry 210compares the speech envelope signal to two thresholds. These comparisonsare typically done in parallel but may also be done sequentially. Thissignal is compared to an average noise threshold in order to determinewhether a voice signal from the microphone is present. The signal isalso compared to a desired audible level threshold in order to determinewhether the speech envelope has achieved desired speech peak indicativeof a voice signal level necessary for proper communication. Thesecomparators output pulses indicating whether the speech envelope leveland corresponding speech peaks is above or below their correspondingthresholds. The pulses are input in logic within the thresholdcomparators and improper speech level detection circuitry 210 and asignal is output indicating whether a user is talking and a voice signalis too weak. This output signal is transmitted to an indicator 205(a).

The indicator notifies a telephone headset user that the voice signal atthe microphone is not sufficiently strong (i.e. a low signal-to-noiseratio). The indicator 205(a) may be part of the adapter 105, such as avisual indicator like a light emitting diode (LED), or an auditoryindicator, such as a speaker that generates an audible tone.Alternatively, the indicator 205(a) maybe coupled to the receive linesof the headset speaker, so that the generated tone indicating improperspeech level is output in the headset speaker, and heard directly by theuser.

It is important to note that a low signal-to-noise ratio may beindicative of problems other than a mispositioned microphone. Forexample, a user may be talking too softly into the microphone. As aresult, the indicator 205(a) also serves as a general warning indicatorrepresentative of the signal at the microphone. Therefore, afterperceiving the activated indicator 205(a) (e.g., seeing a light orhearing a tone), the user can re-position the microphone and/or talklouder so as to increase a corresponding signal-to-noise ratio.

FIG. 2B shows a second embodiment of the present invention whereby anindicator 205(b) is external to the telephone adapter 105. As shown, thetelephone adapter 105 includes a third interface 230. The thirdinterface 230 couples the external indicator 205(b) to the improperspeech level detection circuitry 210 within the telephone adapter 105.Examples of the third interface 230 include a fixed line connectionwhereby the external indicator 205 b is electrically coupled to theimproper speech level detection circuitry 210, and a plug in jack (e.g.,mini-8) whereby the indicator 205(b) may be attached or removed byconnecting a plug into the third interface 230. Additionally, the thirdinterface 230 may be a transceiver that transmits a wireless signal tothe external indicator 205(b).

The threshold comparators and the improper speech level detectioncircuitry 210 activates the external indicator 205(b) via the thirdinterface 230. Examples of the external indicator include a light (e.g.,LED) positioned on a stand, a light positioned on the telephone headset,or a tone generator (e.g., speaker). The external positioning of theindicator 205 b allows a user to select a particular indicator as wellas allowing a vendor the option of selling the indicators as “plug-in”modules to the headset adapter. An example of a “plug-in” module isdescribed in U.S. patent application, Ser. No. 09/401,070, entitled“Accessory Interface Bus For Telephone Headset Adapter, filed Sep. 22,1999, the disclosure of which is incorporated herein by reference.

B. General Description of Microphone Position and Speech Level Sensor

FIG. 3 shows a simplified block diagram of the improper speech leveldetection circuitry. This circuitry comprises four stages: a powersupply and input buffer stage 305, a rectification and envelopedetection stage 310, a threshold adjust and compare stage 315, and amisposition detection stage 320. An audio input is coupled to the powersupply and input buffer stage 305 and receives a signal from thetelephone headset 120. The power supply and input buffer stage 305includes a buffer amplifier 325 with a predefined gain. In thisembodiment, the gain is set at 20dB. The amplifier 325 receives a signalfrom the audio input, applies a gain to the signal, and transmits thesignal to the rectification and envelope detection stage 310.

The rectification and envelope detection stage 310 comprises a full-waverectifier 330 and a precision envelope detector 335. The amplifiedsignal received from the power supply and input buffer stage 305 istransmitted to the full-wave rectifier 330. The full-wave rectifier 330converts the amplified signal to an average direct current signalrepresentative of the instantaneous magnitude of the amplified signal.The rectified signal is then transmitted to the precision envelopedetector 335. The precision envelope detector 335 converts the rectifiedinstantaneous magnitude into a short-term average magnitude representingthe speech envelope. This conversion by the precision envelope detector335 allows independent control of the attack and decay characteristicsof the rectified signal. The speech envelope signal is transmitted tothe threshold adjust and compare stage 315.

The threshold adjust and compare stage 315 comprises two comparators. Afirst comparator 345 determines whether the speech envelope level isabove a background noise threshold. A second comparator 340 determineswhether voice peak levels in the speech envelope cross an audiblethreshold level required for proper communication. As mentioned above,these comparisons are typically done in parallel but may also be donesequentially.

The background noise threshold typically represents the ambient noiselevel of the environment in which the telephone headset orcommunications device operates. For example, a background noisethreshold for a communications device operating on a warehouse floor isgenerally higher than a threshold for a communications device used in anoffice. This background noise threshold may be fixed or may bedynamically adjusted as the ambient noise changes. An embodiment mayinclude a plurality of fixed background noise thresholds. A switch orkeyboard allows a user to select a specific background noise thresholddepending on the environment in which the communication device is beingused. Another embodiment may provide an adaptive background noisethreshold that dynamically adjusts to a particular environment. A methodin which the background noise threshold may be dynamically adjustedcomprises monitoring a signal received by the communications device. Ifthis received signal is active (i.e., a person on the other side of theconversation is speaking) and the signal from the communication deviceis relatively low (i.e., indicative of a person listening), then thesignal from the communication device likely represents the ambient noiseof the environment in which the communication device is operating. Thelevel of this signal may then be used to set a relatively accurate noisethreshold level.

The speech envelope is received from the rectification and envelopedetection stage 310 and compared to the background noise threshold bythe first comparator 345. If the speech envelope level is above thenoise threshold then the comparator outputs a logical TRUE (e.g., +5 V).This output indicates that a user is speaking into the telephone headsetor communication device. The background noise threshold is usuallyslightly above the ambient noise level in order to minimize erroneousTRUE outputs caused by sudden loud noises. Note that for anoise-canceling microphone this level is significantly lower than for anomni-directional microphone with the same sensitivity to the user'svoice. It is particularly important that the background noise thresholdbe set as low as possible for noise-canceling microphones sincepositioning errors cause a more rapid loss of sensitivity to the user'svoice and detection of the user's voice is necessary for the properoperation of the circuit.

The audible threshold typically represents a required voice signal levelrequired for proper communication. For example, a microphone within atelephone headset requires that a user's voice be at a minimum decibellevel in order for a person on the other side of a conversation to beable to easily hear what is being said. Although this threshold may varydepending on the specific communication device that is used, thethreshold is generally fixed and infrequently adjusted. The speechenvelope is received from the rectification and envelope detection stage310 and speech peaks within the speech envelope are monitored by thesecond comparator 340 to determine whether they cross the audiblethreshold. If these speech peaks cross the audible threshold then thesecond comparator 340 outputs a logical FALSE (e.g., 0 V). This outputindicates that the voice signal is sufficiently strong at a microphonein a telephone headset or communication device. However, while the levelof the speech envelope, including speech peaks therein, remains belowthe audible threshold, then the second comparator 340 outputs a logicalTRUE.

Both outputs are transmitted to the misposition detection stage 320comprising a first retriggerable monostable 350, a non-retriggerablemonostable 355, a second retriggerable monostable 365, and various logicgates. The misposition detection stage 320 receives the outputs from thefirst comparator 345 and the second comparator 340 and determineswhether a voice signal is not sufficiently strong at a microphone in atelephone headset or communication device.

A normal speech envelope takes time to develop to its peak amplitude. Ifa simple “AND” function is used to identify a weak voice signal, atemporary misposition or improper speech level indication will occurbefore the audible threshold is reached, be interrupted by the signalfrom the second comparator 340, then will resume as the envelope decaystoward the noise threshold. In addition, the indicator 380 will flashonly for the interval that the signal exceeds the noise threshold and beblanked only for the time it is actively above the audible threshold.For very low speech or severe mispositioning these flashes may be toobrief to be obvious. While transient outputs of the AND gate for lowlevel speech could be stretched, the transient outputs during the attackand decay of normal speech would also be stretched, giving steady falseindications for all normal speech.

According to one embodiment, the non-retriggerable monostable 355 isprovided to inhibit an improper speech level or microphone mispositionindication for a period of time required by a speech envelope to developand reach the audible threshold. For example, the non-retriggerablemonostable 355 may suppress an indication for 100 ms allowing the speechenvelope to reach the audible threshold. After this interval, if thesignal is still between the two thresholds, an indication is activatedshowing that the audible threshold has not been exceeded for a certainperiod of time by various peaks within the speech envelope. This processwill be described in greater detail below.

The dynamics of speech are such that extreme variation in momentaryspeech level exists even within speech that is perceived overall to benormal in level. The duration and interval between speech peaks variesinversely with their intensity, which means that the higher the audiblethreshold is set, the less frequently it will be exceeded. Typically,speech is found between these speech peaks and the speech between thepeaks is of insufficient strength to prevent false misposition orimproper speech level indications. This requires that the inhibitingeffect of the peaks be set to at least extend over the duration of thedecay of the envelope of a phoneme. In practice it was found that evensignificantly mispositioned microphones would exhibit enough peaks tolimit the usefulness of the display if the threshold and time constantwere set low enough to be treated on a phoneme basis. This was due tothe large variations in the intensity of individual phonemes, which inturn requires a fairly low audible threshold to avoid regular falseindications during normal speech. When a time constant was extended tocover several words worth of duration and the audible threshold raisedso that only occasional phonemes would cross threshold, false microphonemisposition or improper speech level detection became less common andreliable detection was improved.

The first retriggerable monostable 350 is implemented to set the amountof time before another speech peak is expected to cross the audiblethreshold. Since speech peaks are only expected to cross the audiblethreshold occasionally, and speech between thresholds is expected to bepresent over most of that interval, it is necessary to inhibit theimproper speech level indication until the next peak is overdue. Theamount of time is dependent on the level selected for the audiblethreshold since detection using lower thresholds can be expected tooccur more frequently. For example, the first retriggerable monostable350 may provide a 3 second time constant during which the output of animproper speech level indication is prevented, even if there is detectedspeech above the background noise threshold and below the audiblethreshold. Speech peaks within the speech envelope signal that cross theaudible threshold will reset the improper speech level indicator 380,terminating any activated improper speech level indication andpreventing any new indication for an established duration of timerelative to the time constant. This process will be described in moredetail below.

The second retriggerable monostable 365 provides a minimum duration forwhich the indicator 380 is activated. This second monostable 365prevents the indicator 380 from flickering on and off, and also ensuresthat the indicator 380 is turned on a sufficient duration so that a userwill notice the indication. For example, the second monostable 365 mayrequire that an initiated indication stay on for a minimum time periodof 1 second. If the voice signal remains weak during this interval theindication will persist without interruption.

An AND gate 360 has inputs coupled to the first retriggerable monostable350, the second comparator 345, and the non-retriggerable monostable355. The AND gate 360 will output a logical TRUE when a detected voicesignal is too weak and the inverted pulse from the non-retriggerablemonostable 355 has passed (i.e., the initial time delay is complete).

An OR gate 370 has inputs coupled to the AND gate 360 output and thesecond retriggerable monostable 365. The output of the OR gate 370 iscoupled to the indicator 380 and turns it on if either input is high. Asa result, as long as the retriggerable monostable is firing or the ANDgate output is a logical TRUE, then the indicator 380 is activated. Aspreviously described, the indicator 380 may be visual (e.g., an LED) orauditory (e.g., a beep).

FIG. 4A is a graphical representation of a weak voice signal at amicrophone within a telephone headset or communication device that isdetected by various embodiments of the present invention. A noisethreshold 400 is shown at a particular decibel (dB) level. An audiblethreshold 410 is shown at another particular dB level. A speech envelopelevel 430 is shown tracing a generic speech pattern 430. At a specificpoint of time t₁ 420, the speech pattern 430 crosses the noise threshold400. At this moment of time t₁, the output on the first comparator 345will go high indicating that a user is talking. In response, thenon-retriggerable monostable 355 will output an inverted pulsesuppressing a microphone misposition or improper speech level indicationfor a period of time required for the speech envelope to develop. At thesame moment of time t₁, the second comparator 340 will be highindicating that a speech peak has not crossed the audible threshold andwill remain high until a speech peak crosses this threshold. The firstretriggerable monostable 350 output will remain high (presuming that ithad not been activated by a previous speech peak), enabling theindicator 380 to activate after the initial suppression time period haspassed. In this instance, the speech peaks within the speech envelope donot cross the audible threshold 410, but remain between the noisethreshold 400 and the audible threshold 410. As a result, according tothis embodiment, the indicator 380 will be activated after the initialsuppression time has passed since the output on the first comparator 345remains high.

FIG. 4B is a graphical representation of a non-talking event that isdetected by various embodiments of the present invention. The noisethreshold 400 is shown at a particular dB level, and the audiblethreshold 410 is shown at another particular dB level. A speech envelope430 is shown tracing a generic speech pattern 430. The speech envelope430 does not cross the noise threshold 400. As a result, the output onthe first comparator 345 remains low. This low output drives the outputon the AND gate 360 to low resulting in the indicator 380 never beingactivated.

FIG. 4C is a graphical representation of a voice signal of sufficientstrength at a microphone on a telephone headset or other communicationdevice that is detected by embodiments of the present invention. Aspeech envelope 430 is shown tracing a generic speech pattern. At afirst point of time t₂, the speech envelope 430 crosses the noisethreshold 400. As described above, the first comparator 345 goes highwhile the second comparator 340 remains high. However, thenon-retriggerable monostable 355 suppresses an initial microphonemisposition or improper speech level indication until the speechenvelope can develop. At a second point of time t₃, the speech envelope430 crosses the audible threshold 410. This second point of time occursbefore the indication suppression time has expired so there has not beena indication prior to the second point of time t₃. At the second pointof time t₃, the second comparator 340 goes low causing the firstretriggerable monostable 350 to output an inverted pulse of a certaintime period. This pulse will drive the output on the AND gate 360 tozero and prevent any indication. However, as long as speech above thenoise threshold 400 is present, another speech peak within the speechenvelope needs to cross the audible threshold 410 within the time periodof this pulse in order to prevent a indication. In this example, asecond speech peak 460 crosses the audible threshold 410 before thepulse time period expires. The time remaining before the pulse will endis reset to the time period of the pulse. As a result, the indicator 380is not activated between the two speech peaks even though the speechenvelope drops below the audible threshold 410 during this timeinterval.

C. Description of Misposition/Improper Speech Level Detection Components

FIG. 5 is a detailed diagram of the misposition detection stagecircuitry 320. As previously described, the non-retriggerable monostable355 has an input that receives the first comparator's output 505. Thenon-retriggerable monostable 355 is also coupled to a first RC circuitcomprising a capacitor 540 and at least one resistor 545. The timeconstant on the inverted pulse generated by the non-retriggerablemonostable 355 is equal to the time constant of a first attached RCcircuit which is the capacitance of the first capacitor 540 multipliedby the effective resistance of the at least one resistor 545. Forexample, if a desired time constant of the inverted pulse is 100 ms,then a 1 μF capacitor and an effective resistance of 100 kΩwould providethe desired time constant. The non-retriggerable monostable 355 isactivated when the first comparator 345 determines that the speechenvelope level has crossed the noise threshold. Once activated, thenon-triggerable monostable 355 outputs a single inverted pulse with acorresponding time constant. This inverted pulse is transmitted to theAND gate 360 and drives the output on the AND gate 360 to low. As aresult, a microphone misposition or improper speech level indication isinhibited for a period of time equal to the time constant on thenon-retriggerable monostable 355.

The first retriggerable monostable 350 has an input that receives thesecond comparator's output 507. The first retriggerable monostable 350is coupled to a second RC circuit comprising a second capacitor 525 andat least one resistor 530. The time constant on the inverted pulsegenerated by the first retriggerable monostable 350 is equal to the timeconstant of the second RC circuit. For example, if a desired timeconstant of the inverted pulse is 3 s, then a 1 μF capacitor and aneffective resistance of 3 MΩ would provide the desired time constant.The first retriggerable monostable 350 is activated when the secondcomparator 340 determines that a speech peak of the speech envelopesignal has crossed the audible threshold. Once activated, the firstretriggerable monostable 350 outputs a single inverted pulse with thecorresponding time constant. An additional speech peak crossing theaudible threshold as the pulse is being transmitted will retrigger themonostable 350. This new trigger re-starts the time period from zero,thereby extending the length of the inverted pulse. As a result, theinverted pulse may continue as long as the first retriggerablemonostable 350 is retriggered within its corresponding time constant.This inverted pulse is transmitted to the AND gate 360 and a reset onthe second retriggerable monostable 365. As a result, the output on theAND gate 360 is driven low as long as a speech peak crosses the audiblethreshold within the time constant of the first retriggerable monostable350. However, if a speech peak does not cross within this time constant,then the output on the first retriggerable monostable 350 goes high andallows the output on the AND gate 360 to go high unless the output onthe non-retriggerable monostable 355 is suppressing the indicator 380 orthe first comparator 345 has already gone low.

The second retriggerable monostable 365 is coupled to the output of theAND gate 360 and its reset is coupled to the output of the firstretriggerable monostable 350. As described above, the secondretriggerable monostable 365 provides a minimum time period for whichthe indicator 380 is activated. This time period is equal to the timeconstant of the attached third RC circuit comprising a third capacitor550 and a third resistor 555. The time constant on the pulse generatedby the second retriggerable monostable 365 is equal to the time constantof the third RC circuit. For example, if a desired time constant of thepulse is 1 s, then a 1 μF capacitor and an effective resistance of 1 MΩwould provide the desired time constant. The second retriggerablemonostable 365 is activated when the output on the AND gate 360 is high.Once activated, the second retriggerable monostable 365 outputs a singlepulse with the corresponding time constant. This pulse is transmitted toan OR gate 370 driving the output of the OR gate high for at least thetime duration of the pulse's time constant. The OR gate 370 is alsoconnected directly to the output of the AND gate 360 so that the outputwill remain high even after the pulse from the second retriggerablemonostable 365 has expired should the output of the first comparator 505remain high while the output of the second comparator 507 also remainshigh. Should the output of AND gate 360 make a transition from low tohigh during a pulse this new trigger re-starts the time period fromzero, thereby extending the length of the pulse. Therefore, the pulsemay continue as long as the second retriggerable monostable isretriggered within its corresponding time constant. As a result, anindication is activated any time the output of the AND gate 360 goeshigh (i.e. the voice signal is between the two thresholds) and theminimum time period of the activated indication is controlled by thetime constant of the second retriggerable monostable 365 (providing thatit is not terminated by the first retriggerable monostable 350). Thesecond retriggerable monostable's reset input is coupled to the outputof the first retriggerable monostable 350. Should the firstretriggerable monostable 350 go active, the second monostable 365 willbe reset, terminating any existing pulse and preventing any new pulsefor as long as the reset remains low.

D. Method for Sensing Microphone Misposition and Speech Level

FIG. 6 shows a simplified flowchart describing a method for sensing avoice signal level at a microphone on a telephone headset. This methodmay be implemented by the foregoing described hardware, or itsequivalents, or by a digital signal processor (DSP) suitably programmed.According to this method, a signal is generated at the microphone andtransmitted to the sensing device. The sensing device receives 600 thesignal and determines whether the signal is sufficiently strong. Thesignal level is compared 605 to a noise threshold to determine whether aheadset user is talking. The signal level is also compared 610 to anaudible threshold to determine whether the signal is sufficiently strongto provide quality reception at the other end of the telephone call.Thereafter, the comparisons are analyzed 620 to determine whether (1)the user is talking and (2) the voice signal is too weak. If the user istalking and the voice signal is too weak, then an indicator is activated630. Typically, this indication is caused by the microphone on theheadset being mispositioned. The indicator is activated for a period oftime and then the method restarts 635. However, if the headset user isnot talking or the voice signal is sufficiently strong, then theindicator is not activated and the method restarts 625.

FIG. 7 shows a detailed flowchart of a method for detecting andindicating a weak voice signal at a microphone in a telephone headset orother communication device. As is the case with FIG. 6, this method maybe implemented by the foregoing described hardware, or its equivalents,or by a digital signal processor (DSP) suitably programmed.Additionally, the method is depicted as having multiple steps performedin parallel; however, the steps may also be performed sequentially.

As shown in FIG. 7, a signal is generated at a microphone andtransmitted to an amplifier 700. The amplified signal is converted 705to a speech envelope using a full-wave rectifier and precision envelopedetector. As previously described, the full-wave rectifier converts theamplified signal to a unipolar signal representing the instantaneousmagnitude of the amplified signal. The precision envelope detectorconverts the instantaneous magnitude of the rectified signal to ashort-term average magnitude, thereby creating the speech envelope. Thisspeech envelope is compared to first threshold to determine whetherspeech is present in the signal from the microphone and to a secondthreshold in order to determine whether the strength of the signal atthe microphone is sufficiently strong to enable proper communication.

The speech envelope level is compared 710 to a noise thresholdrepresenting average ambient noise of the environment in which themicrophone is operating. This comparison determines whether a user istalking. If the speech envelope level is above the noise threshold 715,the length of time that it has been above the threshold is compared to adefined time interval (called X in the diagram). If the signal is abovethe noise threshold and that interval of time has passed since itcrossed the noise threshold, the other conditions for misposition orimproper speech level indication will be evaluated. If either conditionis false, input monitoring will continue. The time interval (X) from thetime when the signal crosses the threshold prevents false indications byignoring noise peaks and giving the speech peaks within the speechenvelope time to develop before an indication is generated. If thespeech envelope level remains below the noise threshold then condition715 remains false, further evaluation does not occur and inputmonitoring continues.

If the speech envelope is above the background noise threshold, speechpeaks within speech envelope are compared 720 to an audible thresholdrepresenting a speech level required at the microphone for propercommunication. This comparison determines whether a microphone ismispositioned, a user is speaking too softly, or other causes of a weakvoice signal at the microphone. If a speech peak crosses the audiblethreshold then a misposition indication is suppressed for a period oftime (Y). If an additional speech peak crosses the audible thresholdduring this suppression period, the period of time is re-initialized tozero 725. However, if a speech peak has not crossed the audiblethreshold within a certain period of time (Y), then an indicator 380 isactivated 730, for a minimum length of time (Z) determined by condition735. Should a speech peak cross the audible threshold while theindicator 380 is active, the indication will be deactivated 740 untilthe conditions 715 and 725 both evaluate to true.

As will be understood by those familiar with the art, the invention maybe embodied in other specific forms without departing from the spirit oressential characteristics thereof. For example, the particular divisionof functionality between the various modules, circuits, or componentsmay differ from that described herein, given the variety of softwarehardware platforms that may be used to practice the invention. Forexample, the hardware implementations include custom ASICs, discretelogic, FPGAs, PLAs, or DSP with appropriate software programming.Finally the particular naming of the circuit elements is not mandatoryor significant, and the mechanisms that implement the invention or itsfeatures may have different names or formats. Accordingly, thedisclosure of the present invention is intended to be illustrative, butnot limiting, of the scope of the invention, which is set forth in thefollowing claims.

1. A telephone headset adapter, comprising: a headset interface adaptedto couple a headset to a telephone, and to receive a speech signal froma microphone on the headset; and a speech level sensing circuit coupledto the headset interface to receive the speech signal from the headsetinterface, and adapted to determine whether a speech level at themicrophone is at an improper level, and provide an output signal inresponse to the occurrence of an improper speech level.
 2. The telephoneheadset adapter of claim 1 further comprising a visual indicator coupledto the speech level sensing circuit, the visual indicator adapted tovisually indicate an improper speech level at the microphone.
 3. Thetelephone headset adapter of claim 2 wherein the visual indicator is alight emitting diode positioned on the headset adapter.
 4. The telephoneheadset adapter of claim 2 wherein the visual indicator is a lightemitting diode positioned on the headset.
 5. The telephone headsetadapter of claim 2 wherein the visual indicator is a light emittingdiode that is a plug-in accessory for the headset adapter.
 6. Thetelephone headset adapter of claim 1 further comprising a tone generatorcoupled to the speech level sensing circuit, the tone generator adaptedto generate a tone in response to an improper speech level at themicrophone.
 7. The telephone headset adapter of claim 1 wherein theoutput signal is provided without providing a feedback signal of theinput signal to a speaker on the headset.
 8. The telephone headsetadapter of claim 1 wherein the speech level sensing circuit detects animproper speech level by comparing the speech signal level at themicrophone to a noise threshold and an audible threshold.
 9. Thetelephone headset adapter of claim 8 wherein the noise threshold isdynamically set.
 10. The telephone headset adapter of claim 9 whereinthe noise threshold is set using an ambient noise level on a signal fromthe telephone headset during a period of time that a user is nottalking.
 11. The telephone headset adapter of claim 8 wherein the speechlevel sensing circuit further comprises: a first comparator adapted todetermine whether the speech signal level is above a noise threshold; asecond comparator adapted to determine whether the speech signal levelis below an audible threshold; and an indicator coupled to the first andsecond comparators, the indicator adapted to indicate that a speechsignal is at an improper level in response to the speech signal levelbeing above the noise threshold and below the audible threshold.
 12. Thetelephone headset adapter of claim 11 further comprising indicatorcontrol logic having a first input coupled to the first comparator, asecond input coupled to the second comparator, and an output coupled tothe indicator, the indicator control logic adapted to activate theindicator for a minimum time period in response to an improper speechlevel.
 13. The telephone headset adapter of claim 11 further comprisingfirst logic device having an input coupled to the first comparator andan output coupled to the indicator, the first logic device adapted toprovide a period of time to permit a speech peak to develop beforeenabling the indicator.
 14. The telephone headset adapter of claim 11further comprising a second logic device having an input coupled to thesecond comparator and an output coupled to the indicator, that monitorsspeech peaks within a speech signal to determine whether a speech signallevel is above the audible threshold.
 15. The telephone headset adapterof claim 14 wherein the detection of a speech peak, within the speechsignal, that is above the audible threshold inhibits an improper speechlevel indication for a period of time following the detection of thespeech peak.
 16. A method for detecting an improper speech signal levelat a microphone, the method comprising: receiving a speech signal fromthe microphone; determining whether a microphone user is talking bycomparing the speech signal level to a noise threshold; determiningwhether the speech signal level is improper by comparing the speechsignal level to an audible level; and activating an indicator when thespeech signal level is between the noise threshold and the audiblethreshold.
 17. The method of claim 16 wherein the microphone is part ofa telephone headset.
 18. The method of claim 16 wherein an improperspeech level is visually indicated to a user.
 19. The method of claim 18wherein a light emitting diode positioned on a headset adapter is usedto visually indicate an improper speech signal level.
 20. The method ofclaim 18 wherein a light emitting diode positioned on the headset isused to visually indicate an improper speech signal level.
 21. Themethod of claim 18 wherein a light emitting diode that is a plug-inaccessory for a headset adapter is used to visually indicate an improperspeech signal level.
 22. The method of claim 16 wherein an improperspeech signal level is audibly indicated to a user.
 23. The method ofclaim 16 wherein an improper speech level indication is provided withoutproviding a feedback signal to a speaker on the headset.
 24. The methodof claim 16 further comprising the step of delaying an improper speechsignal indication for a period of time to allow a speech envelope todevelop.
 25. The method of claim 23 further comprising the step ofproviding a minimum period of time in which the indicator remainsactivated after detecting an improper speech level.
 26. The method ofclaim 16 wherein speech peaks within the speech signal are monitored todetermine whether the speech signal level is below the audiblethreshold.
 27. The method of claim 26 wherein detection of a speechpeak, within the speech signal, that is above the audible thresholdinhibits an improper speech level indication for a period of timefollowing the detection of the speech peak.
 28. The method of claim 16wherein the noise threshold is dynamically set.
 29. The method of claim28 wherein the noise threshold is set using an ambient noise level on asignal from the microphone during a period of time that a user is nottalking.